A substrate processing apparatus typically includes a processing chamber that accommodates a wafer for a semiconductor device (hereinafter simply referred to as “wafer”) as a substrate, and a shower head provided in an upper portion of the processing chamber. In such a substrate processing apparatus, a processing gas is supplied into a processing space within the processing chamber through a plurality of gas holes of the shower head, and the wafer is subjected to plasma processing by means of plasma generated from the processing gas in the processing space.
FIG. 7 is a schematic sectional view showing a structure of a shower head included in a conventional substrate apparatus.
A shower head 70 includes a ceiling electrode plate 71 made of a conductive material, an electrode plate holder 72 for holding the ceiling electrode plate 71, and an internal space 73 provided within the electrode plate holder 72. One end of a gas introducing pipe 74 through which a processing gas is introduced into the internal space 73 is connected to the internal space 73. In addition, a plurality of gas supplying holes 75 and 76 which penetrates through the ceiling electrode plate 71 to allow the internal space 73 to communicate with a processing chamber (not shown) is formed in the ceiling electrode plate 71. In the shower head 70, the processing gas introduced into the internal space 73 through the gas introducing pipe 74 is supplied into a processing space through the gas holes 75 and 76.
However, in such a shower head 70, since the processing gas in the internal space 73 is injected from the gas introducing pipe 74 in the downward direction of the figure, the amount of processing gas passing through the gas hole 75 located immediately below the gas introducing pipe 74 is relatively large while the amount of processing gas passing through the gas holes 76 is relatively small. In this case, since the processing gas cannot be uniformly supplied through the gas holes 75 and 76 into the processing space, plasma generated from the processing gas cannot be uniformly distributed on a wafer. On this account, a surface of the wafer may not be subjected to uniform plasma processing, and as a result, it becomes difficult to secure in-plane uniformity of the plasma processing.
In this connection, there has been proposed a substrate processing apparatus provided with a shower head having buffer plates arranged within its internal space.(see, e.g., Japanese Patent Laid-open Publication No. H-11-054440) In such a shower head, the buffer plate 77 is disposed to face an opening of the gas introducing pipe 74 in the internal space 73 (see FIG. 8). The buffer plate serves to diffuse the processing gas injected from the gas introducing pipe 74 in the internal space 73 in a horizontal direction of the figure while preventing the processing gas from directly flowing through the gas hole 75. This prevents the amount of processing gas passing through the gas hole 75 from extremely increasing and allows the processing gas to be uniformly supplied through the gas holes 75 and 76 into the processing space.
However, there is a case where the thickness (in the vertical direction of the figure) of the shower head 70 is limited and the height of the internal space 73 cannot be sufficiently secured. In this case, the buffer plate 77 is disposed within the internal space 73 and the internal space 73 is divided into an upper space and a lower space. However, the height of both of the upper and lower spaces is extremely lowered, it becomes difficult to increase a conductance with regard to a horizontal flow (diffusion) of the processing gas. As a result, since the processing gas in the internal space 73 cannot be sufficiently diffused in the horizontal direction, the processing gas cannot be uniformly supplied into the processing space, thereby still making it difficult to secure in-plane uniformity of plasma processing for the wafer.